Method of carbonizing spent cooking liquor from pulp making



June 12, 1962 A. M. THOMSEN' 3,038,334

METHOD OF CARBONIZING SPENT COOKING LIQUOR FROM PULP MAKING Filed May 6. 1959 J' ant M3,,

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United States Patent 3,938,834 I METHOD OF CARBONIZING SPENT COQKING LIQUOR FROM PULP MAKING Alfred M. Thomsen, 265 Buckingham Way, Apt. 402, San Francisco, Calif. Filed May 6, 1959, Ser. No. 811,457 3 Claims. (Cl. 162-16) In various co-pending applications I have made use of a carbonized, or coked, product consisting of an intimate mixture of the salts pertaining to such a material commingled with finely divided carbon. In general, when I use the name spent cooking liquor I refer to the neutral or alkaline cooks. The acid cook, with the bi-sulphite of some base is not excluded, however. If lime be the base, or magnesia, then the resultant coke would have but a limited use, but if the base be soda or potash it is quite satisfactory. Also, if the conventional lime based sulphite liquor be treated with sodium sulphate or sodium carbonate, and the lime compound formed removed, then such a liquor is equally suitable. In the applications above referred to I have presented various uses for the carbonized material. In the instant application I present the specific Way in which such material is advantageously prepared, with special emphasis on the recovery of the volatile substances produced during said carbonization. It should be understood that such carbonization bears no resemblance to wood distillation. Unlike the latter, no tar is formed but in place thereof a yellow, mobile oil. Acetic acid is absent, likewise, the principal volatiles being methanol, acetone, and butauone.

In the drawing I have illustrated my process in complete detail. Minor variations are, of course, possible, but to achieve optimum results it is essential that no step be omitted. Such being the case, the best way to understand my process is to follow the drawing step by step. In so doing I shall simultaneously describe any special type of equipment needed and make comments upon the use of same. By thus explaining my drawing I have also given a full and complete description of my process so that any person with adequate knowledge of the technique involved can duplicate my results with ease. Such technique will consist of experience in wood distillation, evaporation and drying, and in the mechanical handling of the conventional still.

Carbonizing a spent cooking liquor must be preceded by a drying step. To dry spent cooking liquor is very difliculit. The step I have introduced, and with which my drawing commences, is to absorb said liquor in the pores of a pre-formed type of carbon which is a re-cycled product obtained in carbonization. At the start, I substitute cornminuted charcoal, but later on the re-cycled product is far superior. This is not a new technique, it is currently found in the literature, but so far as I known no advantage has been taken thereof on a working scale. The reason for this anomaly is that there really is very little use for carbonized cooking liquor.

In the saturator, therefore, I have indicated the formation of a saturated coke by commingling a re-cycled coke with the spent cooking liquor, evaporated to the desired consistency. This will vary with the type of liquor involved, but will, in general, be somewhere between a low of 30% solids, and a high of 50% solids. With the denser liquor there is a great tendency to agglomeration in large lumps during subsequent drying, so adjustment must be made by actual tests in practice.

Any type of a drier may, of course, be used but I prefer a revolving cylinder or kiln, operated with heat and charge in parallel, not in counter-current, flow. In this manner, a relatively high temperature, as much as 1100 F., may safely be used in the entering heating gas stream, while the exit gases are easily brought down as low as 350 F. Very high capacity is thus obtained.

The dried product is then carbonized in a retort. Any type rendered conventional in wood distillation may be used from the antiquated Worm and pipe type to a modern Stafford. The one requirement is that it must have a continous feed and a continuous discharge, so that the exo-thermic feature of carbonization may be fully employed. From this device issues a continous flow of vapors and gas through one vent, while carbonized material is discharged through another vent. Inasmuch as the entering charge is not only dry but pre-heated, nothing is required but the heat developed in this exo-thermic reaction to keep the retort functioning. In fact there is an excess of heat. I control this by re-cycling a certain percentage of the gas discharged from the retort, after it has been stripped of all volatiles by a combination of condensation and cooling with ultimate scrubbing with fresh Water.

In the drawing I have represented the gas and vapors from the retort entering what I have called a condenserevaporator, a device wherein the condensate primarily obtained is re-evaporated without any admixture of permanent gas so that it may be further rectified in a still with its own retained heat. I have represented this first condensation as taking place in an outer jacket, while the condensate thus obtained is transferred to the central space for re-evaporation. Manifestly, this is diagrammatic and does not represent any actual design, but is introduced to explain the principle.

In order to obtain a substantial increase over the yield in standard practice, were that employed, it is essential that the heat in the retort be maintained at the lowest possible degree consonant with the functioning of the exothermic reaction. Even at this low temperature, which may be around 600 F., there is decomposition of the volatiles formed, so it is essential to remove all volatiles as rapidly as possible. Obviously, the introduction of a cool, dry, gas achieves both objects simultaneously. Control, therefore, rests in the volume and temperature of the \gas re-cycled to the retort. It may be stated, by way of explanation that there is nothing remarkable in seeing the discharge pipes for vapors from a Stafford retort working on hardwood Waste at a visible red in daylight, indicating a temperature within the retort of well over 1000 F. Such practice cannot but lead to much destruction of valuable materials.

But even this control of heat within the retort is not enough. After the gases pass the condenser they are anything but free from volatiles. The solubility of said volatiles in the gas is influenced not only by temperature but also by the concentration of said volatiles in the condensate itself. The gas leaving the condenser is, therefore, passed into a coke tower irrigated with fresh, cold water. Obviously, in the top of such a device there is no volatiles in the liquid in contact with the gas, while the liquid leaving the base of the tower contains a recoverable amount. For the sake of economy, it is essential that re-distillation of the weak fluid obtained be inexpensive. I have shown that as obtained when said scrubbing liquor is commingled with the principal condensate from. the "condenser-evaporator, and then re-treated in its central part. The over-all result is that a much concentrated product leaves the central part of said device in the form of vapor, substantially free from permanent gas.

I have shown the principal condensate and the product from the coke tower as comrnin gling in a device called a separator. This may be just a settling tank, or better a centrifuge, in which separation is made between the yellow oil mentioned previously and the watery product containing the methanol, acetone, and butanone. Manifestly, the separation of such material means that a reice fined product is obtained when the vapors leaving the condenser-evaporator are further treated, or rectified, in the still shown at the bottom of the drawing. I regard the separation of the three volatiles from one another as a conventional procedure, while the treatment of the oil, with its phenolic content, is definitely outside of the scope of this disclosure. Having thus fully described my process, I claim:

1. The method of carbonizing spent cooking liquor from pulp making which comprises; absorbing said liquor to substantial saturation in the pores of a preformed recycled coke produced at a later step; drying the resultant mixture of coke and cooking liquor; carbonizin g said dried material by means of the inherent exothermic reaction; controlling the heat of said reaction by re-cycling a cooled, dry gas, originating in said carbonization after it has been stripped of condensable volatiles; condensing the gas and vapors emanating from said carbonization thus obtaining permanent gas and a condensate; re-cycling that portion of said permanent gas as previously prescribed as the controlling factor in carbonization; re-evaporating the volatiles in said condensate by the heat resident in the gas and vapors emanating from the carbonization step; rectifying the vapors thus obtained into methanol, acetone, and butanone, and a Watery reject.

2. The method of carbonizing spent cooking liquor from pulp making set forth in claim 1, with the added step that the permanent gas, after condensation, be further purified from contained methanol, acetone, and butanone by scrubbing with fresh water, the scrubbing medium, after such use, being comrningled with the condensate previously obtained and re-evaporated in the manner previously specified.

3. The method of carbonizing spent cooking liquor from pulp making set forth in claim 1, with the added step that separation be made between the oily components and the watery components of the condensate obtained therein prior to the reevaporation of the watery portion in the manner therein described.

References Cited in the file of this patent UNITED STATES PATENTS 1,315,889 Westin Sept. 9, 1919 1,900,506 Kumler Mar. 7, 1933 2,334,620 Goodell Nov. 16, 1943 

1. THE METHOD OF CARBONIZING SPENT COOKING LIQUOR FROM PULP MAKING WHICH COMPRISES; ABSORBING SAID LIQUOR TO SUBSTANTIAL SATURATION IN THE PORES OF A PREFORMED RECYLCED COKE PRODUCED AT A LATER STEP; DRYING THE RESULTANT MIXCTURE OF COKE AND COOKING LIQUOR; CARBONIZING SAID DRIED MATERIAL BY MEANS OF THE INHERENT EXOTHERMIC REACTION; CONTROLLING THE HEAT OF SAID REACTION BY RE-CYCLING A COOLED, DRY GAS, ORIGINATING IN SAID CARBONIZATION AFTER IT HAS BEEN STRIPPED OF CONDENSABLE VOLATILES; CONDENSING THE GAS AND VAPORS EMANATING FROM SAID CARBONIZATION THUS OBTAINING PERMANENT GAS AND A CONDENSATE; RE-CYCLING THAT PORTION OF SAID PERMANENT GAS AS PREVIOUSLY PRESCRIBED AS THE CONTROLLING FACTOR IN CARBONIZATION; RE-EVAPORATIGN THE VOLATILES IN CONDENSATE BY THE HEAT RESIDENT IN THE GAS AND VAPORS EMANATING FROM THE CARBONIZATION STEP; RECTIFYING THE VAPORS THUS OBTAINED INTO METHANOL, ACETONE, AND BUTANONE, AND A WATERY REJECT. 